Professor Steven Chu, former Energy Secretary under President Obama, delivered the 2014 S T Lee Lecture on 10 November at the University of Cambridge. Science and technology such as the industrial and agricultural revolutions have profoundly transformed the world. In his talk, Professor Chu will first discuss an “epidemiological” approach of assessing the risks of climate change, and then provide a perspective on how we can mitigate the risks with science, technology and policy, so that sustainable energy becomes the low cost option.